It is well known that ellipsometer, polarimeter and the like systems allow determination of sample system physical and optical properties, (such as thickness, refractive index and extinction coefficient of surface films thereon), by detecting change in "Polarization State" and/or Intensity of a beam of polarized light which is caused to interact with said sample system, where Polarization State here refers to a set of values for Polarized Light Beam Orthogonal Components, (such as "S" and "P"), Magnitude Ratio, and a Phase Angle therebetween. (It is noted that "P" refers to that component which is in a plane containing the normal to a sample system and incident and/or transmitted beam(s) of polarized light, and "S" refers to that component perpendicular thereto and parallel to the surface of said sample system. It is also noted that a "full" polarization state also requires designation of an absolute value to which a magnitude ratio is referenced, and the direction of rotation of a polarized beam of light).
As general background, it should be appreciated that ellipsometer systems can be broadly classified as:
1. Rotatable Element or Intensity Modulating Rotating Element Ellipsometers (REE); and PA1 2. Phase Modulating Modulation Element Ellipsometers (MEE). PA1 a. a first system comprising two pairs of reflecting means as described infra herein; PA1 b. a sample system; and PA1 c. a second system comprising two pairs of reflecting means as described infra herein; PA1 a. providing a system for changing the initial propagation direction of a beam of electromagnetic radiation without significantly changing the phase angle between orthogonal components thereof, such as just described; PA1 b. causing an initial beam of electromagnetic radiation to impinge upon the first reflecting means in the first pair of reflecting means and reflect therefrom; PA1 c. accessing a resulting beam of electromagnetic radiation with a changed direction of propagation which reflects from the second reflecting means in the second pair of reflecting means. PA1 a. providing a material system investigating system comprising elements selected from the group consisting of: PA1 b. causing said light source and a polarizer to produce a first generally horizontally oriented propagation direction polarized beam of electromagnetic radiation; PA1 c. causing said first generally horizontally oriented propagation direction polarized beam of electromagnetic radiation to interact with said first optic element and become a first generally vertically oriented propagation direction polarized beam of electromagnetic radiation which is caused to pass through a first focusing optic and interact with a material system placed upon said material system stage; PA1 d. causing a second generally vertically oriented propagation direction polarized beam of electromagnetic radiation provided by said first generally vertically oriented propagation direction polarized beam of electromagnetic radiation interaction with said material system to pass through a second focusing optic and interact with a second optic element, in which second optic element said second generally vertically oriented propagation direction polarized beam of electromagnetic radiation is caused to become a second generally horizontally oriented propagation direction polarized beam of electromagnetic radiation; PA1 e. causing said second generally horizontally oriented propagation direction polarized beam of electromagnetic radiation to pass through said analyzer and said aperture and enter detector system;
An example, for instance, is presented in a Patent to Woollam et al., U.S. Pat. No. 5,373,359, which describes a Rotating Analyzer Ellipsometer (RAE) in which a Light Source provided beam of light is caused to pass through a Polarizer, (which serves to set a Porarization State therein), then interact with a sample system. Said interaction with said sample system serves to alter the Polarization State of said polarized beam of light, which polarized beam of light then sequentially encounters a Rotating Analyzer and a Dispersion Optics, (eg. a Diffraction Grating is specified), which forms therefrom a multiplicity of essentially single wavelength polarized beams of light. Said multiplicity of essentially single wavelength polarized beams of light are then caused to enter a Photo Detector Array, in which Photo Detector Array, individual Detector Elements serve to develop a representative signal for each. Fourier Analysis, for instance, of said signals allows determination of parameters which allow determination of sample system characterizing PSI and DELTA values. It is noted that in said Woollam et al. (RAE) there is no additional focusing applied after the polarized beam of light encounters the sample system. Additional Patents to Johs et al. and Green et al., U.S. Pat. Nos. 5,504,582 and 5,521,706 respectively provide further insight into rotating analyzer ellipsometer systems.
Another Patent, U.S. Pat. No. 5,416,588 to Ducharme et al., describes a Modulation Element Ellipsometer (MEE) comprised of a Light Source, a Polarizer, a Polarization State Modulator Element, a means for splitting Orthogonal Components in a Beam of Polarized Light after interaction with a sample system, two Detector Elements and an Analysis system. In use a beam of light is provided by the Light Source and a state of Polarization is set therein by said Polarizer, after which the polarized beam of light is subjected to a Polarization State Modulation and caused to interact with a sample system, which sample system changes the State of Polarization of said Phase Modulated Polarized beam of light. Orthogonal Components of said Polarized beam of Light are then isolated and subjected to separate, for instance, Fourier Analysis. Appropriate utilization of the Coefficients of the terms of a Fourier Series allows determination of sample system characterizing PSI and DELTA values. It is noted the described Modulation Element Ellipsometer (MEE) utilizes Coefficients from Fourier Series based upon both Orthogonal Components. Some Modulation Ellipsometers utilize Fourier Series Coefficients from only one such Orthogonal Component. While the specifics of signal generation are different in (REE) and (MEE) ellipsometers, and even amongst Ellipsometers of similar type, the end result of utilization thereof is provision of PSI and DELTA values for sample systems analyzed therein.
Generally, the present invention can be applied to essentially any ellipsometer or polarimeter and the like system, and provides a solution to a problem in the use thereof which presents when a sample system is to be investigated with a polarized beam of electromagnetic radiation which is initially oriented in a propagation direction other than appropriate to cause it to impinge upon a sample system, and in which space constraints prevent reorienting the source of the initially oriented polarized beam of electromagnetic radiation.
One application of the present invention is identified in co-pending U.S. patent application Ser. No. 09/033,694. Said 694 Application describes a system wherein a beam of electromagnetic radiation is to be made to impinge upon a sample system at an angle-of-incidence which is beyond, (eg. 65 degrees), a typical Brewster Angle, which Brewster angle is near seventy-five (75) degrees in most semiconductors. A typical range of angle-of-incidence over which the present invention can be applied is between thirty (30) and eighty (80) degrees from a normal to a sample system surface, with a range of deviation from a Brewster angle of between five (5) and ten (10) degrees being of particular relevance. It is noted that the present invention provides convenient means by which to achieve a smaller electromagnetic beam "Spot" size, (which accompanies a smaller angle-of-incidence on an investigated material system). The present invention also enables realization of laterally-compact ellipsometer or polarimeter and the like systems.
With an eye to the present invention, a Search of Patents was conducted, with the result being that very little was found. A Patent to Kasai, U.S Pat. No. 3,874,797 is disclosed, however, as it describes a system for directing an electromagnetic beam utilizing totally reflecting prisms. As well, a Patent to Lange, U.S. Pat. No. 4,801,798 is disclosed as it describes a system which utilizes electromagnetic beam directing reflective means in a system which causes an electromagnetic beam to impinge upon an investigated sample system at an angle very near to a perpendicular to a surface thereof. A Patent to Smith, U.S. Pat. No. 4,381,151 is also disclosed as it describes a system in which numerous reflections of a light beam occur.
A paper titled "Division-Of-Amplitude Photopolarimeter Based on Conical Diffraction For a Metallic Grating" by Azzam, in Applied Optics, Vol. 31, No. 19, Jul. 1, 1992 and U.S. Pat. No. 5,337,146 are also noted. While the system described in said references is somewhat relevant, the purpose of the System and Method of Use described in said references is to allow simultaneous measurement of all four Stokes Parameters of a Beam of Light.
It is also noted that the reference titled "ELLIPSOMETRY AND POLARIZED LIGHT", by Azzam and Bashara, North-Holland, 1977 is incorporated by reference into this Disclosure for the purpose of providing general information regarding sample analysis systems utilizing electromagnetic beams, and fundamentals of electromagnetic beams.
In view of known prior art, it is apparent that a system, and method of its use, which would allow a user of a sample analysis system such as a ellipsometer, polarimeter or a functionally similar system, to investigate sample systems with beams of electromagnetic radiation which are initially not oriented in a propagation direction appropriate to effect interaction with a sample system, or at non-optimal angles-of-incidence with respect to a normal to a material system surface, without requiring major system reconfiguration procedures be performed, which system and method allow changing the propagation direction of the initial beam of electromagnetic radiation without changing the phase angle between orthogonal components thereof, would be of great utility. The present invention provides such a system and method of its use.